Hydrogen fuel, which can be obtained from fuels such as natural gas, methanol, or petroleum, and oxygen from the air electrochemically combine in the fuel cell to produce electricity. Heat and pure water vapor are the only by-products from the fuel cell's electrochemical reaction.

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Above: A schematic of the Proton Exchange Membrane (PEM) Fuel Cell  (Ballard Power Systems)

Proton Exchange Membrane (PEM) Fuel Cell

The fundamental component of the Ballard® fuel cell consists of two electrodes, the anode and the cathode, separated by a polymer membrane electrolyte. Each of the electrodes is coated on one side with a thin platinum catalyst layer. The electrodes, catalyst and membrane together form the membrane electrode assembly.

Hydrogen fuel dissociates into free electrons and protons (positive hydrogen ions) in the presence of the platinum catalyst at the anode. The free electrons are conducted in the form of usable electric current through the external circuit. The protons migrate through the membrane electrolyte to the cathode. At the cathode, oxygen from air, electrons from the external circuit and protons combine to form pure water and heat. Individual fuel cells produce about 0.6 Volt and are combined into a fuel cell stack to provide the amount of electrical power required.

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	Above: An illustration of the Ballard Fuel Cell (Ballard Power Systems)

Parts of a Ballard fuel cell

A single fuel cell consists of a membrane electrode assembly and two flow field plates.  Single cells are combined into a fuel cell stack to produce the desired level of electrical power.

Each membrane electrode assembly consists of two electrodes (anode and cathode) with a thin layer of catalyst, bonded to either side of a proton exchange membrane (PEM).

Gases (hydrogen and air) are supplied to the electrodes on either side of the PEM through channels formed in the flow field plates. Hydrogen flows through the channels to the anode where the platinum catalyst promotes its separation into protons and electrons. On the opposite side of the PEM, air flows through the channels to the cathode where oxygen in the air attracts the hydrogen protons through the PEM.

The electrons are captured as useful electricity through an external circuit and combine with the protons and oxygen to produce water vapor on the cathode side.

Reprinted courtesy of Ballard Power Systems